JP2001238323A - Coaxial cable and its forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coaxial cable that is stable, even in the environment in which the extreme change of temperature occurs, and a simple method and device for forming the end of the coaxial cable. SOLUTION: A cable 10 consists of a center line conductor 12, an insulating material 14 formed with several layers of PTFE tapes and a metal-braided external conductor 16. The external conductor 16 is cut off in an appropriate length to expose the insulating material. A shroud 20 is slid into the external conductor. The shroud 20 has a spacer lip, that contacts the end of the external conductor and a gap is formed between the lip and the exposed insulating material. Then, the end of the cable 10 is inserted into the blind hole 32 of a tool and heated. The blind hole is fitted on the outside circumference of the insulating material, being shorter than the insulating material in diameter. The tool is pushed onto the cable 10 and compresses the insulating material, until it contacts the spacer lip. The heat of the tool melts the several layers of the PTFE tapes altogether, causes the PTFE tapes to flow, and forms beads in the gap inside the space lip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a terminal of a coaxial cable, and more particularly to a method for fixing both ends of an outer conductive layer and an inner dielectric (insulating) layer.

[0002]

2. Description of the Related Art Coaxial cables consist essentially of a central conductor, typically a metal wire, a dielectric (insulator) spacer,
It consists of an outer conductor, typically a metal braid (braid), and a protective jacket. The insulator spacer can be made of unsintered or partially sintered polytetrafluoroethylene (PTFE). PTFE
Is generally extruded or taped onto the center conductor and is typically surrounded by three layers, one to one, around the center conductor.
It is spirally wound with 0 layers. Such unsintered or partially sintered PTFE dielectric (insulator) is hereinafter referred to as “expanded PTFE” (ePTFE).

[0003]

However, many applications, especially in space flight, require flexible high performance microwave cables to operate in extreme temperature ranges. Due to power, multi-paction, return loss (impedance mismatch), and phase matching issues, cable and conductor component placement is stable,
It is important that the relative position does not change. Any change in size and dielectric constant can severely affect the microwave characteristics of the cable assembly. Because of the variety of materials used to manufacture these cable assemblies, it is not possible to guarantee that the various layers of material will not move within the cable under extreme temperature changes. Was.

This movement is mainly caused by a large difference between the coefficient of thermal expansion of the ePTFE dielectric (insulator) and the coefficient of thermal expansion of the metal conductor. In particular, when a coaxial cable is manufactured using ePTFE tape as the insulator, the cable insulator tends to recede at both ends of the cable under repeated high and low temperature cycles. As a result, a gap is created between the insulator of the cable and the insulator block forming part of the connector at the end of the cable. The sudden change in the dielectric constant at both ends of this gap significantly impairs microwave transmission along the cable.

[0005]

SUMMARY OF THE INVENTION To avoid this potential and significant problem, the insulation must be mechanically secured to other parts of the cable. Until now, there is no simple fixing method that solves the above problem without significantly reducing the high frequency electrical performance. The present invention comprises a bead that sinters the different PTFE layers together so that they do not move relative to each other at the end of the cable, and engages the ends of the metal blades so that the PTFE does not recede into the braid. The purpose is to form an outer layer.

In accordance with one aspect of the present invention, there is provided a method of forming a coaxial cable termination. The cable has a center and outer conductor separated by an insulator. The insulator extends from the end of the outer conductor and is exposed. The exposed insulator is compressed in the axial direction while being restricted in the radial direction. The insulator radially expands in a region adjacent to the outer conductor end to form beads having an outer diameter greater than the inner diameter of the outer conductor.

According to another aspect of the invention, there is provided a coaxial cable having a center and an outer conductor separated by an insulator, wherein at least one end of the insulator is longer than a corresponding end of the outer conductor. And a coaxial cable formed with an annular bead protruding radially adjacent the end of the outer conductor sufficient to prevent the insulator from retracting into the outer conductor. provide.

The step of expanding the insulator defines a gap between the two axially separated components, and
Extending the insulator into the gap.
The width of the gap is determined by the spacer, then
The beads are preferably formed radially inside the spacer, leaving free space between the formed beads and the spacer. One of the two components separated on the axis is the outer conductor of the cable, and one of them is a member that radially regulates the exposed insulator. Can be. The latter can be heated heating means if the insulator is a thermoplastic resin.

In accordance with yet another aspect of the present invention, there is provided an apparatus for forming a terminal of a coaxial cable. The device has a spacer lip sized to fit the outer conductor of the cable, and at one end is sized to abut an end of the outer conductor; and A shroud made of a refractory material radially defining a gap from the outer surface of the body, sized to slide over the insulator of the cable, and sized to abut the spacer lip of the shroud. With blind holes,
Heated means for heating.

The insulator is made of a thermoplastic resin, especially PTFE.
And can be heated sufficiently to soften. If the insulator is wrapped as a tape or otherwise formed in multiple layers, it is preferred that the heating be sufficient to melt the exposed layers of the insulator into an integral body.

After formation, the beads, at the transition between the melted and unmelted layers of the insulator,
It can be shaped to reduce the effects of any impedance changes. Preferably, the effect of a transition with the shaped beads is less than, preferably less than half, the impedance of a similar transition without the beads.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Referring first to FIG. 1, one embodiment of a coaxial cable for transmitting microwave signals is indicated generally by the reference numeral 10. The cable 10 is essentially a central conductor 12, which is a metal wire, a dielectric (insulator) spacer 14, which is a spirally wound or extruded multi-layer ePTFE tape, a metal braid. A certain outer conductor 1
6 and a protective jacket 18. In the first step of the molding method according to the invention, each layer is trimmed to provide a clean end perpendicular to the length of the cable and to expose a length of layer there. . In particular, the blade 16 is stripped to expose a substantial length of ePTFE.

Referring now also to FIG. 2, in a second step of the molding method, a ceramic shroud, generally designated by the reference numeral 20, is slid onto the treated end of the cable 10. As shown in FIG. 2, the main body of the shroud 20
It is composed of a cylindrical tube (cylindrical body) 22 that is loosely fitted around the exposed blade 16. FIG. 4 (B)
As will be shown in more detail in the following, a shoulder 24 is provided at the rear end of the shroud, which fits more tightly on the exposed blade 16 and provides accurate centering of the shroud and cable ( Centering). A lip 26 is provided at a position beyond the shoulder 24,
The lip portion 26 extends radially inward so as to sufficiently overlap with the blade 16. The lip 26 does not extend to contact the exposed dielectric or insulator 14, but rather leaves a sufficient gap 28 in the radial direction. The radial width of the gap 28 is typically at least 2% of the outer diameter of the blade 16. Shroud 2
0 is positioned so that the lip 26 abuts the cut end of the blade 16.

Referring now to FIG. 3, the sintering head, generally designated by the reference numeral 30, is configured largely as a cylindrical titanium block with a heating member (not shown). The sintering head 30 has a cable 1 at one end.
A blind hole 32 having a diameter suitable for sliding on the outer periphery of the exposed insulator 14 is provided. The depth of the hole 32 is about half the length of the exposed portion of the insulator 14. The sintering head 30 also
It has an axial through-hole 34 which is large enough to receive the central conductor 12 of the cable 10. An ignition pin 36 is received in a hole provided in the radial direction of the sintering head 30, and if the center conductor 12 is present in the hole 34, it is in a position to clamp the center conductor 12. It is possible to move forward. The sintering head 30 is at least 375 ° C. (700 ° F.)
Preheated to a temperature below 00 ° F). As shown in FIG. 3, the sintering head 30 is first placed at the end of the cable 10, whereby the cut end of the insulator 14 abuts against the bottom surface of the blind hole 32 and the end of the central conductor 12 penetrates. It fits in the hole 34.

Referring now to FIG. 4A, the sintering head 30 is then pressed against the end of the cable 10,
The insulator 14 is compressed. At this time, the cable 10 is held by at least one cable grip 35. The cable grip 35 is located at least 7 mm (0.25 inch) retracted from the exposed blade 16 portion. The blade 16 is fitted on the insulator 14 with sufficient tension so that the insulator 14 is not pushed into the blade by the sintering head 30. The sintering head is advanced until it contacts the lip 26 of the shroud 20, as shown in FIG. The gap 28 is thus a closed annular space axially between the blade 16 and the sintering head 30 and radially between the insulator 14 and the lip 26.

As shown in FIG. 5A, the sintering head 30
Is then secured in place by tightening the ignition pin 36 to the center conductor 12. Thereby, the sintering head 3
Good thermal contact between 0 and the center conductor 12 is ensured.
Within the heated sintering head, the ePTFE forms a continuous member 42. ePTFE expands and the sintering head 3
0 blind hole 32 is filled. Since ePTFE presses against the surface of the blind hole, good heat transfer is ensured. FIG. 5 (B)
The ePTFE then flows into gap 28 to form beads 40, as shown in FIG. The time for which the sintering head is heated on the cable depends on the characteristics of the cable, but is typically between 20 seconds and 3 minutes. FIG. 5 (B)
As shown in FIG. 5, the beads 40 are not filled in the gaps 28, and the space exists outside the beads. This allows the joint to flow completely around the blade and achieves good joint filling. Heating also eliminates the previous shape memory of the PTFE and ensures that the beads are permanent.

The entire assembly is subsequently cooled, and then the titanium sintering head 30 and ceramic shroud 20 are removed from the cable. As shown in FIG. 6A, the sintered PTFE body 42 shrinks, but the beads 40 are still large enough to secure the blade ends. The blades are not embedded in the sintered PTFE, but the beads are large enough that they cannot slide inside the blades. The beads 40 are formed as shown in FIG. 6B by providing a bevel 44 at the lip of the hole 32 of the sintering head 30 as shown in FIG. 6A. Can be.

The sintering of ePTFE, of course, changes the dielectric constant. In particular, the sintered ePTFE 42 at the end,
A rapid change in the dielectric constant occurs between the blade 16 and the ePTFE 14 which is only partially sintered. Such changes generally occur at the location of the bead 40 and can be corrected by shaping the bead and / or by shaping the inside of the metal cable connector fitted to the bead. Since the change inside the braid 16 between the partially sintered ePTFE 14 and the unsintered ePTFE 14 is extremely slow,
It does not seriously affect microwave transmission. The sintered ePTFE 42 at the end can also be shaped mechanically and electrically to optimally fit the connector.

Referring now to FIGS. 7 and 8, a conventional coaxial cable connector, generally designated by the reference numeral 50, is attached to the end of the cable 10.

The sleeve 52 of the connector 50 is attached to the cable 10 and covers the exposed portion of the blade 16 and the end of the jacket 18. The sleeve 52 is mechanically and electrically fixed to the blade 16 by soldering. An outer threaded collar 54 is provided on the sleeve 52.
Fixed behind the shoulders 56. Metal connector pin 5
8 is fitted to the exposed end of the center conductor 12 of the cable 10 and forms the center pin of the connector 50. The pin 58 is fixed behind the shoulder of the insulating sleeve 60, and the insulating sleeve 60 is
2 fixed behind the shoulder, the sleeve 62
Is screwed into. An internally threaded collar 64 forming the mating component on the outside of the connector 50 is attached to the sleeve 62 using spring ring means 66 and held rotatably.

As shown in FIG. 7, the transition from the bead 40 and thus the sintered insulator 42 to the only partially sintered insulator 14 is the transition between the blade 16 and the connector sleeve 52. Aligned with parts. As shown in FIG. 8, the beads 40 are machined into a shape that corrects for transitions in other elements, thereby
The microwave signal along or through the connector 50 can be propagated with as little disturbance as possible.

Although the present invention has been described with reference to the embodiments,
Various modifications will occur to those skilled in the art without departing from the scope of the invention.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional side view of a coaxial cable, shroud, and sintering head prepared to form a cable termination.

FIG. 2 is a view similar to FIG. 1 showing a shroud arranged on a cable.

FIG. 3 is a view similar to FIG. 2 showing the sintering head engaging the end of the cable;

4 (A) is a view similar to FIG. 3 showing the latter half of the terminal forming method, and FIG. 4 (B) shows “FIG. 4 (B)” in FIG. 4 (A); It is a detailed enlarged view of the circular part shown as.

5 (A) is a view similar to FIG. 4 (A) showing the final step of the terminal forming method, and FIG. 5 (B) is FIG. 5 (A).
It is a detailed enlarged view of the circular part shown as "FIG. 5 (B)" in it.

FIG. 6 (A) is a view similar to FIG. 5 (A) showing the shaped cable removed from the sintering head.
(B) is a detailed enlarged view of the circular portion shown as “FIG. 6 (B)” in FIG. 6 (A).

FIG. 7 is a longitudinal sectional view of a coaxial cable connector fitted to the cable formed as shown in FIGS. 1 to 6;

FIG. 8 is a detailed enlarged view of a circular portion shown as “FIG. 8” in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Coaxial cable 12 Center conductor 14 Insulator 16 Metal braid (outer conductor) 18 Protective jacket 20 Shroud 28 Gap 30 Sintering head 32 Blind hole 34 Through hole 40 Bead 42 Sintered insulator 50 Connector

Continuing on the front page (72) Inventor Joseph N. Caulfield 19014 Aston Apartment H-4 Penel Road 224 Pennsylvania United States

Claims (17)

[Claims] 1. A method of forming an end of a coaxial cable, comprising: a coaxial cable having a center and an outer conductor separated by an insulator, wherein the insulator extends from an end of the outer conductor and is exposed. Providing a cable, compressing the exposed insulator in an axial direction while restricting the insulator in a radial direction, and expanding the insulator in a radial direction in a region near an end of the outer conductor. Forming a bead having an outer diameter larger than the inner diameter of the outer conductor. 2. The step of extending the insulator includes defining a gap between two axially separated components and extending the insulator into the interior of the gap. The method of claim 1, wherein: 3. The width of the gap is determined by a spacer, and the beads are formed radially inside the spacer, leaving free space between the formed beads and the spacer. 3. The method of claim 2, wherein: 4. The method of claim 2, wherein one of said two components is said outer conductor of said cable. 5. The method of claim 2, wherein one of the two components is a member that radially regulates the exposed insulator. 6. The method of claim 1 wherein said insulator is a thermoplastic and said method includes heating said insulator sufficiently to soften said insulator. 7. The method of claim 6, wherein said insulator comprises PTFE. 8. The insulator comprises a plurality of layers, and
7. The method of claim 6, wherein the method comprises heating the insulator sufficiently to melt the exposed layers of the insulator into a single piece. 9. The method of claim 6, further comprising the step of shaping the beads so as to reduce the effect of any change in impedance at a transition between the melted and unmelted layers of the insulator. 9. The method of claim 8, wherein the method comprises: 10. The method further comprises inserting the exposed insulator into a blind hole of a tool to be heated, axially compressing the insulator at a wall of the hole, and radially isolating the insulator. 7. The method of claim 6, further comprising the step of regulating in a direction. 11. A coaxial cable having a center and an outer conductor separated by an insulator, wherein at least one end of the insulator protrudes axially from a corresponding end of the outer conductor; A coaxial cable characterized in that an annular bead is formed that protrudes radially adjacent an end of the outer conductor enough to prevent the body from retracting into the outer conductor. 12. The coaxial cable according to claim 11, wherein said beads are formed by plastic flow of said insulator. 13. The insulator is a thermoplastic resin,
13. The coaxial cable of claim 12, wherein the beads are formed by hot flow of the insulator that has been sufficiently heated and softened. 14. The coaxial cable according to claim 13, wherein said insulator is PTFE. 15. The semiconductor device according to claim 15, wherein the insulator is formed of a plurality of layers, and the plurality of layers are melted together at a position where the insulator protrudes from an end of the outer conductor. 13 coaxial cables. 16. The bead is shaped to reduce the effect of any change in impedance in the transition region between the melted and unmelted layers of the insulator. Item 15. The coaxial cable according to Item 15. 17. Apparatus for shaping the end of a coaxial cable, the spacer being sized to fit into the outer conductor of the coaxial cable and having at one end a dimension to abut the end of the outer conductor. A shroud made of a refractory material having a lip portion and defining a radial gap from an outer surface of the insulator of the cable; and a dimension slidably fitted to the insulator of the cable; and A heated tool having a blind hole dimensioned to abut the spacer lip of the shroud.